$vw_design: 750;
$vw_fontsize: 75;

//
@function rem($width) {
  @return ($width / $vw_fontsize) * 1rem;
}

html {
  font-size: ($vw_fontsize / $vw_design) * 100vw; //10vw

  // iphone4 是 320px
  @media screen and (max-width: 320px) {
    // 锁定的最小 1rem = 32px
    font-size: 32px;
  }

  @media screen and (min-width: 540px) {
    font-size: 54px;
  }
}

.box {
  width: rem(430);
  height: rem(280);
  font-size: rem(28);
  border: 1px solid #222;
}

.border {
  border-top: rem(1) solid red;
}

.img-wrapper {
  margin: 0 auto;
  width: rem(440);
  img {
    display: block;
    width: 100%;
    height: auto;
  }
}


